The Flow Cytometry Service provides Cancer Center researchers with access to state-of-the-art flow cytometric equipment including a Becton-Dickinson (BD) FACStar cell sorter, a single-laser BD FACScan analyzer, and a dual-laser BD FACSCalibur analyzer. Service personnel have extensive expertise in current cytometric applications and also manage and distribute customized reagents from the Service's monoclonal antibody resource. Flow Cytometry is operated on a first-come, first-served basis offering services through either assisted or unassisted access. Through assisted access, Flow Cytometry staff offers preparation of cells, nuclei, or chromosomes for analysis or sorting on the appropriate flow cytometer. As part of this service, Cancer Center staff and the experienced technical staff of the Service develop a protocol that is then carried out by the Flow Cytometry staff. Upon completion of the experiment, the technicians are available to assist with data analysis in association with the researcher. The Service also assists researchers with the design of protocols using a variety of existing and newly developed dye compounds, and in parallel the Service offers custom reagent preparation employing these dyes. Through unassisted access, trained users independently acquire and analyze data as needed with Service's technical support available at all times. Flow Cytometry has been supported by the Cancer Center support grant for 18 years, and is an integral component of research at the Cancer Center. Use of this Service has increased 23 percent since the first year of the current CCSG funding period. To meet the increased user demand and operate additional cytometry instrumentation, additional technical labor was added during the current five-year CCSG period. Derry C. Roopenian, Ph.D., an immunologist, has served as the Scientific Staff Supervisor since 1991. Dr. Roopenian communicates regularly with the User Group and service personnel to insure that users have equitable service access and that their needs are met in the most efficient, cost effective and technically current manner.